Such apparatus is inter alia known from international patent application WO 95/16377. In this known apparatus, a small-bubbled foam layer is obtained by the increased speed of the liquid jet. The liquid flows directly from the outlet to the outflow opening. However, the character of the small-bubbled foam layer obtained, i.e. the distribution of the size of the different bubbles, proves to be little uniform and predictable. From this international patent application, it is also known to provide the outflow opening, rather than the inlet, with a spout opening. Accordingly, the apparatus spouts directly into, for instance, a cup. However, this variant also has the above-outlined drawbacks.
The object of the invention is to meet this problem and is characterized in that in the liquid flow path extending between the spout opening and the outflow opening, a buffer reservoir is incorporated, spaced from the spout opening and the outflow opening, the buffer reservoir being positioned such that, in use, the coffee extract jet from the outlet spouts into a liquid surface of coffee extract already received in the buffer reservoir.
If a coffee extract is fed to the inlet under relatively low pressure, the spout opening of the inlet generates a coffee extract jet. This coffee extract jet ends up in the buffer reservoir, so that the buffer reservoir will be filled with a quantity of coffee extract. Due to the fact that the coffee extract jet spouts into the liquid surface of the meanwhile filled buffer reservoir, bubbles will be formed in the buffer reservoir. At the same time, at least a portion of the coffee extract having bubbles will flow from the buffer reservoir to subsequently flow from the apparatus via the outflow opening. Since the liquid jet spouts into the buffer reservoir, a small-bubbled foam layer is obtained whose properties are predetermined.
Gebrauchsmuster 29502575 discloses an apparatus for preparing coffee extract having a small-bubbled foam layer, comprising at least one inlet for coffee extract and one outflow opening for discharging coffee extract having a small-bubbled foam layer. In this known apparatus, two outflow openings are present in a bottom. Disposed on the bottom is a spherical element covering the two outflow openings. The spherical element consists of vertical sidewalls and a spherical top wall, with a number of orifices being provided in the vertical sidewalls. In use, a coffee filter filled with ground coffee, which filter consists of a bowl-shaped element manufactured from rigid material, is placed between the inlet and the spherical element. Next, the apparatus is connected to a high-pressure coffee apparatus. Under a pressure of for instance 7 bar, the coffee apparatus feeds hot water to the coffee filter in the apparatus. In the coffee filter, the ground coffee is compressed to form a compact whole. This involves a high pressure being built up in the coffee filter. As a result, the coffee extract is forced out via the openings in the bottom of the coffee filter. During the forcing out of the coffee extract, bubbles are formed in a space between the bottom of the coffee filter and the top wall of the spherical cover. Bubbles smaller than the section of the orifices of the spherical cover can then flow away from the apparatus via the outflow openings in the bottom. In this manner, via these outflow openings, a coffee extract is dispensed which can be received in a cup disposed under the assembly. In the cup filled with coffee extract, a foam layer will be present on the coffee extract.
A drawback of the assembly known from Gebrauchsmuster 29502575 is that for forming the bubbles, it is necessary to build up a high pressure in the apparatus. This implies that for pressurizing the apparatus, relatively expensive means, such as an electric pump, are required.
The object of the invention is to provide an apparatus whereby a coffee extract having a small-bubbled foam layer can also be prepared under low pressure.
According to a further elaboration of the invention, the flowing away of coffee extract with bubbles from the buffer reservoir can for instance be effected in that the buffer reservoir overflows. However, it is also possible that the buffer reservoir is provided with at least one run-out opening for discharging coffee extract with a small-bubbled foam layer from the buffer reservoir to the outflow opening. This has the advantage that after the preparation of the coffee extract having a small-bubbled foam layer, no or only little residual liquid stays behind in the buffer reservoir. In particular, the buffer reservoir is of bowl-shaped design, with the run-out opening provided in a sidewall of the buffer reservoir.
It is also possible that the buffer reservoir is of bowl-shaped design while a bottom of the buffer reservoir is provided with at least one run-out opening for discharging coffee extract having a small-bubbled foam layer from the buffer reservoir to the outflow opening.
According to another aspect of the invention, which also provides a solution to the above-mentioned problems in respect of the apparatuses of the prior art, a buffer reservoir is incorporated into the liquid flow path extending between the spout opening and the outflow opening, which buffer reservoir is spaced from the spout opening and comprises the outflow opening mentioned, while, in use, the buffer reservoir is positioned such that, in use, the coffee extract jet from the spout opening spouts into a liquid surface of coffee extract already received in the buffer reservoir, and the quantity of coffee extract dispensed through the spout opening per unit of time and the quantity of coffee extract flowing from the buffer reservoir via the outflow opening per unit of time are adjusted to each other so that in the buffer reservoir a liquid surface is formed having a height of at least 5 mm.
Because the coffee extract jet spouts into the coffee extract both located in the buffer reservoir with a height of at least 5 mm, the jet striking the bath involves the formation of a small-bubbled foam layer. Via the outflow openings, this small-bubbled foam layer is entrained with the rest of the coffee extract to subsequently flow into a container. Preferably, the quantity of coffee extract dispensed through the spout opening per unit of time and the quantity of coffee extract flowing via the outflow opening from the buffer reservoir per unit of time are adjusted to each other so that in the buffer reservoir a liquid surface is formed having a height of at least 8 mm.
According to a preferred embodiment of the invention, the apparatus further comprises a Neopolitana unit for preparing the coffee extract, the Neopolitana unit being in fluid connection with the inlet. The Neopolitana unit has the characteristic feature of dispensing a coffee extract under a relatively low pressure of, for instance, 0.4 atmosphere. In combination with the spout opening of the inlet and the buffer reservoir, this low pressure is sufficient for obtaining a coffee extract having a small-bubbled foam layer.
The Neopolitana unit preferably comprises a hermetically closable liquid container, a coffee container that can be filled with ground coffee, a liquid-conveying tube connected on one side to the coffee container and comprising on the other side an open end located adjacent a bottom of the liquid container, the inlet with the spout opening being in fluid connection with the coffee container such that, in use, the ground coffee is located in the liquid flow path from the liquid container to the inlet.
Because the flavor of the coffee extract is not only determined by the small-bubbled foam layer, but also by the temperature, according to a highly advanced embodiment, the liquid container comprises means for controlling the ration between the quantities of liquid and air in the liquid container without changing the quantity of liquid for setting the temperature of the liquid which, in use, is fed to the coffee container.
The invention also relates to a Neopolitana apparatus characterized in that the liquid container comprises means for controlling the ratio between the quantities of liquid and air in the liquid container without changing the quantity of liquid for determining the temperature of the liquid which, in use, is fed to the coffee container. According to the invention, this method is characterized in that the temperature of the coffee extract is controlled by a selection of the ratio between the quantity of air and the quantity of water present in the filling chamber.